为什么是std :: this_thread命名空间？ [英] Why the std::this_thread namespace?

问题描述

std :: this_thread命名空间有技术原因吗？为什么这个命名空间的成员没有实现为std :: thread类的静态成员？

Is there a technical reason for the std::this_thread namespace? Why could the members of this namespace not have been implemented as static members of the std::thread class?

推荐答案

href =http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2184.html =nofollow>原始提案，获取方法 thread :: id 拼写 get_id（）是否获得 thread :: id 为自己或子线程：

From the original proposal, the way to get a thread::id is spelled get_id() whether you are getting the thread::id for yourself, or for a child thread:

注意使用 this_thread 命名空间来消除歧义，当你是
请求当前线程的id，而子线程的id。
该操作的 get_id 名称保持不变，有利于
减少接口的概念足迹。

Note the use of the this_thread namespace to disambiguate when you are requesting the id for the current thread, vs the id of a child thread. The get_id name for this action remains the same in the interest of reducing the conceptual footprint of the interface.

std::thread my_child_thread(f);
typedef std::thread::id ID;

ID my_id = std::this_thread::get_id();  // The current thread's id
ID your_id = my_child_thread.get_id();  // The child   thread's id

因此 this_thread 命名空间是一种可读的方式来区分两者，同时将概念界面保持最小（获取线程标识的名称相同）。

Thus the this_thread namespace is a readable way to differentiate between the two, while keeping the conceptual interface to a minimum (same name for getting a thread id).

这里有一个可能的替代设计：

Here's a possible alternative design:

struct thread
{
    static int get_id() {return 1;}
    int get_id() const {return 2;}
};

此设计的一个缺点是它不能编译：

One disadvantage of this design is that it does not compile:

test.cpp:4:9: error: static and non-static member functions with the same parameter types cannot be overloaded
    int get_id() const {return 2;}
        ^
test.cpp:3:16: note: previous declaration is here
    static int get_id() {return 1;}
               ^
1 error generated.

另一种设计会给静态成员一个不同的名称。但现在的界面更大了。原来的建议也处理另一个函数完全相同的方式：

Another design would have given the static member a different name. But now the interface is bigger. The original proposal also treated another function the exact same way:

bool have_i_been_canceled = std::this_thread::cancellation_requested();  // Current thread's cancellation status
bool have_you_been_canceled = my_child_thread.cancellation_requested();  // Child   thread's cancellation status

因此，重用这些名称非常有意义，不得不学习这么多的名字。他们只需要学习使用 this_thread 命名空间，如果他们想查询当前线程。不幸的是，委员会在标准化期间取消了线程取消。

Thus it made a lot of sense to reuse the names so clients don't have to learn so many names. They just need to learn to use the this_thread namespace if they want to query the current thread. Unfortunately the committee removed thread cancellation during standardization.

这篇关于为什么是std :: this_thread命名空间？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！